Process And Property Control Mechanisms Of Laser Additive Manufacturing Of CNTs Reinforced Metal Matrix Composites

There is an increasing demand for lightweight,high strength and high performance metallic materials in modern industries.Using carbon nanotubes?CNTs?as reforcing phase to prepare metal matrix composites is an effective route.In this study,carbon nanotubes/aluminum alloy?CNTs/AlSi10Mg?mixed powder and carbon nanotubes/iron-nickel alloy?CNTs/FeNi?mixed powder were used as starting materials to prepare carbon nanotubes reinforced Al matrix composites?CNT/Al?and carbon nanotubes reinforced FeNi matrix composites?CNT/FeNi?by selective laser melting?SLM?.The effects of laser process parameters and CNTs content on the density,phase,microstructure and mechanical properties of the as-fabricated composites were investigated.CNT/Al specimens were fabricated by SLM using various laser power?P?and scan speed?v?.P was the dominant factor affecting the density of as-fabricated specimens.The density increased with the increasing P.When applied P was fixed,the density increased firstly and then decreased as v increased.The CNT/Al consisted of typical cellular structures.Al9Si with some precipitated Si particles were inside the cells,and the cell boundaries consist of eutectic Si.Partially in-situ reacted CNTs existed inside some cells.When applied P was 300 W and applied v was 2000 mm/s,the density of as-fabricated specimen was 99.76%,the microhardness was 154.12 HV_0.2,and the tensile strength and elongation were 420.8 MPa and 8.87%,respectively.The hardness,wear resistance and tensile properties of CNT/Al enhanced with increased applied P.When applied P was 375 W and applied v was 2000 mm/s,the microhardness was 164.28 HV_0.2,the coefficient of friction?COF?and wear rate were 0.21 and 2.75×10^-5 mm³/N m,respectively,and the tensile strength and elongation were 425 MPa and 9.0%,respectively.The hardness,wear resistance and tensile strength of CNT/Al increased with increased CNTs content,while the elongation increased first and then decreased.When the CNTs content was 1.5 wt.%,the microhardness was 170.37 HV_0.2,the COF and wear rate were 0.17 and 2.16×10^-5 mm³/N m,respectively,and the tensile strength was 483.5 MPa.Grain refinement strengthening,second-phase strengthening,dislocation propagation and load transfer were the main strengthening mechanisms for SLM-processed CNT/Al composite parts.CNT/FeNi composite specimens were fabricated by SLM under different laser linear energy densities???.The relative density of as-fabricated specimens increased firstly and then decreased with increased?,the highest density was 99.07%when?was 333.3 J/m.The CNT/FeNi were mainly consisted of cellular grains.The structures at the cell boundaries transferred from Fe₇Ni₃ to Fe₃Ni₂ as the applied?increased,and the chemical composition inside the cells was similar to initial FeNi powder.When applied?was 333.3 J/m,the as-fabricated CNT/FeNi exhibited excellent wear performance,soft magnetic properties and corrosion resistance due to high density and uniform distribution of CNTs.